U.S. Pat. Nos. 2,543,959, Eastin, Mar. 6, 1951, 3,278,320, Neely et al, Oct. 11, 1966, 3,392,037, Neely et al, July 9, 1968, 3,470,004, Begley et al, Sept. 30, 1969, 3,594,199, Treffner et al, July 20, 1971, 3,635,740, Davies et al, Jan. 18, 1972, 3,868,261, Cassens Jr. et al, Feb. 25, 1975.
The U.S. patents listed above are typical of the art known to the inventor at the time this application is filed.
U.S. Pat. No. 2,543,959 shows a magnesia containing cement made from sea water magnesia that has much less density as compared with magnesia produced from ore. The cement includes MgO from seawater and MgCl.sub.2 and fillers together with sodium triphosphate or (NaPO.sub.3)n for example and it is said the phosphate addition minimizes shrinkage as the cement mixed with water, cures. Fillers suggested for use in this cement are sand, ground "lime rock", asbestos and iron oxide.
U.S. Pat. No. 3,278,320 shows a furnace cement for patching the hot lining in steel making furnaces made up of a mixture of chromite ore, magnesia, a bonding agent, a plasticizer, and iron oxide. The chromite ore may contain from 5% to 20% magnesia along with from 1% to 20% silica, 8% to 25% alumina, 15% to 29% iron oxide and 0.1% to 3% calcium oxide. A plastic clay such as bentonite may be used in an amount of from 1% to 3%. The batch includes an iron oxide addition of 100 mesh and finer with 90% passing a 325 mesh screen. A sodium tripolyphosphate bond is employed.
The chrome ore, that may contain a substantial magnesia component, is mixed with periclase that contains upwards of 95% magnesia. Sodium tripolyphosphate, in a small percent, together with bentonite and iron oxide are mixed with the chrome ore and periclase to form a dry mix that is wetted to be gunned onto the hot furnace lining.
In this cement the chrome ore and periclase form the bulk of the refractory composition and the ore and magnesia are reacted together in the thin 1/8" to 1/2" liner applied to the hot surface of the steel furnace to form a monolithic coating.
U.S. Pat. No. 3,392,037 shows a composition used for molding refractory shapes that are said to have superior hot strength. The refractory grain from which the product is made may be periclase, chromite, or mixtures thereof mixed with sodium tripolyphosphate that serves as a binder. The mixture is wetted and pressed to shape and fired to form a brick that shows improved hot strength as a shaped fired brick, but this product is not suggested as a raw batch for a ramming cement.
U.S. Pat. No. 3,470,004 shows a refractory cement for bonding refractory elements made of chromia-magnesia components. For this purpose a mixture of chromia-magnesia spinel together with a plasticizing agent is made up, that includes a sodium silicate, a plasticizing kaolin addition and a wetting agent. The dry ingredients when mixed with water may be troweled into place and it is said that the water carries silicate particles and fused chromia-magnesia into the pores of the surface of the articles to be bonded to improve the bond strength.
U.S. Pat. No. 3,594,199 describes a prereacted chrome ore and magnesia such as periclase that is crushed and mixed with a pigment grade chromic oxide (Cr.sub.2 O.sub.3) in an amount of 2 to 10% based on the weight of the grain. An aqueous binder such as sodium lignin sulfonate is added and the resulting mixture pressed to a desired shape and fired at 2800.degree. to 3800.degree. F. The mix is not suggested for use as a cement.
U.S. Pat. No. 3,635,740 shows another fired refractory shape. It is stated that a dual temperature firing procedure is to be followed to improve the hot strength of a chromia-magnesia brick. The chrome ore and magnesite are crushed and mixed together with a ball clay. A suitable liquid is added and the wet mix is pressed into a brick shape. The green brick is first fired at about 2900.degree. F. and cooled and then fired at 3150.degree. F. It is stated that the silica in the ball clay is distributed during the first firing by reaction with other compounds in the mix so that upon subsequent firing to the higher temperature the silicates do not liquify as has happened in the past. These formulations are made into bricks and no cement mixes are discussed, the invention being concerned with the two stage firing procedure to tie up the silicates.
U.S. Pat. No. 3,868,261 shows a chromia-magnesia spinel mortar that includes an addition of chromia to the mix to control shrinkage when the mortar is heated. No clay or other silicate containing compound is used in this mortar in order to eliminate all lower melting silica containing ingredients. The mix of this disclosure includes prereacted crushed chromia-magnesia 35 mesh and finer and as much as 50% passing 325 mesh to produce volume stability, i.e. to control shrinkage on the subsequent firing of the mortar. An addition of a pure, synthetic Cr.sub.2 O.sub.3 in a finely divided state having an average particle size of 1.5 microns or less is made in an amount of up to 13% to further control shrinkage and it is said that because of the critical degree of fineness of the spinel and amount of pure Cr.sub.2 O.sub.3 present, that volume stability results and shrinkage is controlled. There is no discussion of its troweling or ramming characteristics and the only use for this mortar is shown to be for bonding bricks together.